In real life, there's nothing funny about identity theft, as anyone who's gone through it can attest. (Believe me, I learned the hard way.) Unfortunately, if the new comedy "Identity Thief" is anything to go by, there's nothing funny about it on screen either.

OK, not nothing funny. Let's be generous to director Seth Gordon and screenwriters Craig Mazin and Jerry Eeten and say there's not very much funny here. It's a film built around a simple log line: average nice guy must share a road trip with the resourceful sociopath who has destroyed his credit rating (and pretty much everything else in his life).

The basic notion — two people unwillingly on the road together are forced to get along, eventually realizing each other's worth and learning life lessons — is ancient. In movies, it goes back (at least) to Frank Capra's 1934 romantic comedy “It Happened One Night,” which spawned a number of cookie-cutter imitations. While initially showing strictly male-female pairs, the genre for the last few decades has shown up primarily as male-male films — call them “bromantic comedies.” (There's a doctoral dissertation to be written on why the culture created this gender switch.) “Rain Man” may be the most acclaimed, but the two best remain “Midnight Run” and “Planes, Trains and Automobiles.” (To his credit, producer/star Jason Bateman openly cites these two films as models.)

Apparently “Identity Thief” was originally conceived in accordance with the predominant gender preference, but, following Melissa McCarthy's breakout success in “Bridesmaids,” someone had the very good idea to cast her as the thief. This significantly shifts the tone and some of the themes running throughout. For one thing, the opening really emphasizes Sandy Patterson's beautiful wife (Amanda Peet) and children, to minimize the chance of awkward romantic feelings between Sandy and Diana (McCarthy).

The issue of Diana's largeness — and our cultural assumptions and biases — always lurks in the background, as it often does in McCarthy's roles. (The grand exception would be John August's underappreciated “The Nines,” where it's confronted head-on rather than lurking.) If Sandy were not married, the audience would assume that he fails to respond to her because of her size. In fact, within the story, people take them for a couple and then interpret Sandy's hostility toward her as weight-related.

Luckily, the way the plot is set up, Sandy is hostile for the most legitimate possible reason — Diana is a truly awful person for much of the film. In Sandy's position, most of us would throttle her within five minutes. Of course, she can't stay that way, and the script predictably sets up her redemption. The most impressive element in the whole thing is McCarthy's ability to make us accept her conversion from horrible jerk to sympathetic misfit.

Bateman is certainly the go-to actor these days for pleasant, likable guys in the mold of early Tom Hanks, but he has stronger hints of something less pleasant beneath the surface. (“Juno” would be the best example.) He's a grade-A straight man, and McCarthy is more than madcap enough to provide him with stuff to react to. If only the rest of “Identity Thief” were up to their standard.

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ANDY KLEINis the film critic for Marquee. He can also be heard on "FilmWeek" on KPCC-FM (89.3).